Oxidation of organic compounds



Patented Oct. 31, 1933 OXIDATION OF ORGANIC COMPOUNDS Christoph Beck,

Ludwigshai'en-on-the-Bhine,

and Heinrich Diekinann, Mannheim, Germany, assignors to I. G. Farbenindustrio Aktiengesellsohaft, Frankiort-on-the-Main, Germany, a corporation of Germany in Drawing. Application July 29, 1929, serial No. 382,063, and in Germany August 29, 1928 9 Claims.

The present invention relates to improvements in the oxidation of organic compounds.

When oxidizing organic compounds and especially those of high molecular weight, such as parafiin wax or montan wax, by means of gaseous agents containing oxygen, such as gases or gaseous compounds containing oxygen, in particular when converting parafiin Wax and the like into fatty acids, it is often very important to avoid the formation of hydroxy carboxylic acids and anhydrides and condensation products thereoi which are insoluble in petroleum ether, since these are troublesome in the further working up of the fatty acids formed.

W e have now found that when oxidizing organic compounds of high molecular weight the formation of the said undesirable hydroxy carboxylic acids and the like can be prevented to a great extent by making the working conditions milder as the oxidation of the initial materials proceeds, for example by diminishing the reaction temperature or the concentration of oxygen in the gaseous oxidizing agents or by diminishing both together or by reducing the pressure and/or the velocity of the gases. It has been found that the temperature at which the reaction is carried out is very important, not only for the velocity of the oxidation of the initial material, but also for the extent of the degradation caused by oxidation of the latter. When the greater part of the organic compounds has been converted into carbox ylic acids, the oxidizing action of the gases can be arrested to such an extent by lowering the temperature that no alteration in the carboxylic acids formed occurs, but that the further oxidation is practically restricted to the initial materials. The greater the amount of initial material which has been converted into carboxylic acids during the process, the more it is advantageous to lower the temperature, so that towards the end oi the reaction, when besides small quantities of unchanged initial material the oxidation mixture mainly con= sists of carboxylic acids, the temperature is at its lowest value. temperature is dependent on the composition of the gas or gaseous compound containing oxygen which is employed for the oxidation, on the nature of the organic compound to be oxidized as well as on the activity of a catalyst, such as metal salts of organic acids, for example, zinc or aluminium stearate, metal enolates or metal phosphates and the like, if such be employed.

The oxidizing action of the gas containing oxy gen on the initial material may alsobe iniiu= enced to a greatextent by altering the oxygen The exact height of the reaction content of the gaseous compounds containing oxygen. Thus, for example, the oxidizing action of gases consisting of or containing higher oxides of nitrogen can be rendered much milder by adding to the gas, which may consist mainly of nitrogen dioxide, large quantities of nitrogen monoxide. oxidizing gas may be varied within wide limits, but it has been found particularly advantageous to reduce the oxidizing action of the gas only a little at the beginning oi the oxidation by the addition or not too much nitrogen monoxide, and, as the formation of carboxylic acid progresses, to make the oxidizing action of the gas more and more mild by the addition of larger quantities of nitrogen monoxide. In this manner, for example in the oxidation of paramn wax, the fatty acids already formed can be protected from further degradation caused by oxidation so that practically a complete oxidation of the par amn wax into fatty acids is obtained without the formation oi'hydroxy carboxylic acids and the like.

When employing undiluted oxides of nitrogen for the oxidation, the desired content of nitrogen monoxide can be obtained, for example, by employing liquid nitrogen tetroxide with which some nitrogen trioxide is mixed for the produc: tion of the oxidizing gas. Then, after the initial oxidation, it is preferable only partially to regencrate the waste gases, which have been reduced to nitrogen monoxide, to nitrogen dioxide, so that in the circulating oxidizing gas a certain amount of the nitrogen monoxide formed always remains.

Moreover, the velocity of flow of the oxidizing gases can be so arranged that the concentration of nitrogen monoxide iormed in the reaction is always kept at a desired value in the reaction chamber. For this purpose it is preferable to allow the oxides of nitrogen to iiow through several oxidation vessels arranged one behind the other, of which the first is charged with the most difficultly oxidizable and only slightly attacked initial material, while in the subsequent vessels the already oxidized more sensitive product is exposed to the action or" the oxidizing gases flow ing off from the previous oxidation vessels, the oxidizing action of which gases is much milder in consequence oi their higher content of nitrogen monoxide.

When working in this manner it is often oi particular advantage to regulate the temperature as the composition of the oxidizing gases changes so that at the beginning of the reaction, for ex- The content of nitrogen monoxide in the ample in the first reaction vessel, the oxidation is accelerated as much as possible by employing elevated temperatures, whilst towards the end of the reaction, for example in the later reaction vessels, by maintaining lower temperatures and/ or employing the aforedescribed milder oxidizing agents the fatty acids already formed are further protected from further attack.

The process is equally applicable to compounds of low molecular weight, such as methane and the like to aldehydes, in which process hydroxycarboxylic acids usually do not occur, but in which process the formation of acids is to be avoided.

The following examples will further illustrate the nature of this invention, but the invention is not restricted thereto.

Example 1 100 kilograms of crude paraffin wax having a melting point of 54 C. are oxidized at 110 C. with a gaseous mixture consisting of 90 per cent of nitrogen dioxide and 10 per cent of nitrogen monoxide. After about 50 per cent has been converted into fatty acids, the temperature is lowered to about 90 C., and after per cent of the paraffin wax has been converted, to 60 C. In this manner an oxidation product is obtained which has an acid value of 210 and a saponification value of 280, and which then only contains 8 per cent of unsaponifiable substance. The content oi hydroxy carboxylic acids which are insoluble in petroleum ether is less than 10 per cent, whereas the product obtained without lowering the temperature or reducing the oxygen content of the oxidizing gases contains about 40 per cent.

Example 2 100 kilograms of paraffin wax having a melting point of 54 C. are oxidized by means of concentrated gaseous nitrogen oxides at 70 C. and at a pressure of 5 atmospheres, the gases being passed quickly at first through the paraffin wax, so that the nitrogen oxides are only slightly reduced and the content of nitrogen monoxide in the gases contained in the oxidation vessel is low. When about of the charge is oxidized, the velocity of the current of nitrogen oxides is diminished, so that the content of nitrogen monoxide in the gases flowing from the reaction vessel amounts to about 60 per cent in consequence of the increased oxidizing action. After some time when the oxidation is nearly completed, the velocity of the current of oxidizing gases is further reduced so far that the gases flowing from the reaction vessel contain more' than 90 per cent of nitrogen monoxide. The product obtained possesses an acid value of 220 and a saponification value of 290. the content of unsaponiflable matter amounts to about 10 per cent and the content of hydroxy carboxylic acids to about 6 per cent.

Example 3 The oxidation of paraflin wax having a melting point of 54 C. is performed in a system of 3 autoclaves arranged in series through which the oxidizing gases containing nitrogen dioxide are passed. In the autoclave arranged as the first reaction vessel a temperature of 90 C. and a pressure of 7 atmospheres is maintained, the second autoclave being kept at a temperature of 70 C. and a pressure of 5 atmospheres, the 3rd autoclave at a temperature of 50 C. and at a pressure of 3 atmospheres. The gases introduced into the first autoclave and containing about 10 per cent of free oxygen and 90 per cent of nitrogen dioxide lose during the reaction in the first autoclave such a quantity of oxygen that on entering the second autoclave they contain about 50 per cent nitrogen monoxide and 50 per cent nitrogen dioxide. In the 2nd and 3rd autoclave further quantities of oxygen are consumed, so that the gases contain about 25 per cent of nitrogen dioxide when leaving the second autoclave and only from 5 to 10 per cent when leaving the third autoclave. In the first autoclave the paraflin wax is pumped in a cycle until about 60 per cent of the hydrocarbons are converted into fatty acids, whereupon the mixture is passed over, preferably by pressure, into the second autoclave, in which subsequently a further 20 to 25 per cent of the paraffin wax is oxidized, so that on entering the 3rd autoclave the oxidation product contains only from 15 to 20 per cent of unattacked hydrocarbons. The final product drawn ofi from the 3rd autoclave consists of practically pure fatty acids and has an acid value of about 250 and a saponification value of 295, the content of unsaponifiable matter being less than 5 per cent and the content of hydroxy carboxylic acids only 3 per cent.

. Example 4 American fuel oil is refined with the aid of sulphuric acid and then oxidized with a mixture of air and nitrogen oxides as is obtained in the catalytic oxidation of ammonia. When starting the temperature is kept at 90 C. and the velocity of the gases is 30 cubic meters per hour and per each 100 kilograms of the 011. After 40 per cent of the oil has been oxidized the velocity of the gases is diminshed step by step down to 10 cubic meters per hour and the temperature is simultaneously lowered to 60 C. After 14 hours a mixture of fatty acids is obtained showing an acid value of 280 and a saponiflcation value of 340 and containing but 8 per cent of hydroxy carboxylic acids. By oxidizing without the aforesaid precautions a product with a much higher ester value and a much higher content of hydroxy carboxylic acids is obtained.

Example 5 A current of air is blown at 160 0. through molten paraffin wax at the rate of 1 cubic meter per hour and per each kilogram of the wax until the reaction product shows an acid value of 40 and a saponiflcation value of 120. The tempera ture is then gradually lowered to 130 C. and the Example 6 A gaseous mixture consisting of crude methane (conta ning about 65 per cent by volume of methane) 34 per cent of oxygen and 1 per cent of nitrogen oxide is preheated to from 300 to 400 C. and then passed over a catalytic layer consisting of salts of heavy metals, particularly of metal phosphates, such as mercury and/or iron phosphates. By keeping the catalytic layer at from 550 to 600 C. from 1.5 to 2 per cent of the initial methane is converted into formaldehyde and one half of the reaction product consists of formaldehyde and the other of formic acid. When, however, the space only at which the gases are introduced, is kept at the said tempera ture the remaining catalytic layer being kept at from 450 to 500 C. only, the same quantity of methane is converted, but without the formation of formic acid so that the yieldof formaldehye is considerably increased.

What we claim is:

1. In the process of producing organic acids, which are highly susceptible to oxidation, by oxidizing normally liquid and solid, parafiinic hydrocarbons at from about 60 to about 160 C., with a stream of gas containing oxygen, the step of gradually reducing the strength of the oxidation conditions to which a given batch of said hydrocarbons is being subjected during the oxidation of that batch, thus retarding the oxidation of said organic acids.

2. In the process of producing organic acids, which are highly susceptible to oxidation, by oxidizing normally liquid and solid, parafflnic hydrocarbons at from about 60 to about 160 C., with a stream of gas containing oxygen, the step of decreasing the oxidizing activity of said stream acting on a given batch of said hydrocarbons during the oxidation of said batch, thus retarding the oxidation of said organic acids.

3. In the process of producing organic acids,

which are highly susceptible to oxidation, by oxidizing normally liquid and solid, parafiinic hydrocarbons at from about 60 to about 160 C., with a stream of gas containing oxygen, the step of gradually lowering the temperature to which a given batch of said hydrocarbons is being subjected during the oxidation and decreasing the oxidizing activity of said stream acting on said batch, thus retarding the oxidation of said organic acids. 4. In the process of producing organic acids, which are highly susceptible to oxidation, by oxidizing normally liquid and solid, parafiinic hydrocarbons at from about 60 toabout 160 0., with a stream of gas containing oxygen the step of gradually lowering the temperature to which a given batch of said hydrocarbons is being subjected during the oxidation and decreasing the oxygen content of the said stream acting on said batch, thus retarding the oxidation of said organic acids.

5. In the process of producing organic acids, which are highly susceptible to oxidation, by

oxidizing normally liquid and solid, paraflinic hydrocarbons at from about 60 to about 160 C., with a stream of gas containing nitrogen dioxide the step of decreasing the oxidizing activity of said stream acting on a given batch of said hydrocarbons during the oxidation of said batch, thus retarding the oxidation of said organic acids.

6. In the process of producing organic acids, which are highly susceptible to oxidation, by oxidizing normally liquid and solid, paraffinic hydrocarbons at from about 60 to about 160 C., with a stream of gas containing nitrogen dioxide the step of gradually lowering the temperature to which a given batch of said hydrocarbons is being subjected during the oxidation and decreasing the oxidizing activity of said stream acting on said batch, thus retarding the oxidation of said organic acids.

'7. In the process of producing organic acids, which are highly susceptible to oxidation, by oxidizing normally liquid and solid, parafdnic hydrocarbons at from about 60" to about 160 6., with a stream of gas containing nitrogen dioxide the step of gradually lowering the temperature to which a given batch of said hydrocarbons is being subjected during the oxidation and increasing the content of nitric oxide in the said stream acting on said batch, thus retarding the oxidation of said organic acids.

8. In the process of producing organic acids, which are highly susceptible to oxidation, by oxidizing parafiin wax at from about 60 to about 160 C., with a stream of gas containing oxygen' the step of gradually lowering the temperature to which a given batch of said paraffin wax is subjected during the oxidation of that batch, thus retarding the oxidation of said organic acids.

9. In the process of producing organic acids,

which are highly susceptible to oxidation, by oxidizing paramn wax at from about 60 to about 160 0., with a stream of gas containing nitrogen dioxide, the step of gradually lowering the temperature to which a given batch of said paraffin wax is being subjected during the oxidation of that batch and decreasing the oxidizing activity of said stream acting on said batch, thus retarding the oxidation of said organic acids.

CHRISTOPH BECK. HEINRICH DIEKMANN. 

